NEW YORK (CNNMoney) - While one of Elon Musk's companies is celebrating after launching the world's most powerful rocket into space, another company is fighting for liftoff back on Earth.

Tesla said Wednesday that its losses soared to $675 million in the final three months of 2017, up from $121 million in the same period a year earlier, as the company worked to ramp up production for the Model 3 sedan.

The loss was narrower than Wall Street had expected, however. Tesla's stock was flat in after hours trading Wednesday following the earnings report.

Tesla has struggled to overcome bottlenecks and delays in producing the more affordable Model 3, with the hope of becoming a truly mainstream car maker.

The electric car company continues to predict it will be able to produce 5,000 Model 3 vehicles a week by the end of the second quarter of this year. But it once hoped to reach that goal by the end of 2017.

"It is important to note that while these are the levels we are focused on hitting and we have plans in place to achieve them, our prior experience on the Model 3 ramp has demonstrated the difficulty of accurately forecasting specific production rates at specific points in time," the company wrote in a letter to shareholders Wednesday.

Tesla delivered 1,542 Model 3 vehicles in the quarter, barely making a dent in the reservation list for the new car, as it faced production delays.

But demand for its other two cars, the Model S and X, helped push Tesla's sales to $11.8 billion for 2017, up 55% from the year prior. Tesla expects to deliver about 100,000 of the two models in 2018.

The Tesla earnings report comes one day after Musk's other company, SpaceX, successfully launched the massive Falcon Heavy rocket.

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